Method and apparatus for annealing



May 23, 1933), J SMAIL 1,911,167

METHOD AND APPARATUS FOR ANNEALING Filed May 17, 1950 INVENTOR Patented ay 23, 1933 JAMES A. SMAIL, 0F YG'UNGSTUW, @HIO METHOD AND APP Application filed May '17,

lhis invention relates to the heat treatment' of sheet metal, tin plate, strip, plates, and, in particular, to the box annealing of ferrous sheets and the like.

According to the present practice in box annealing, the material to be treated is piled on the bottom of the box. The top of the box is then lowered and sealed to the bottom and the whole box is placed in the furnace where it is heated to the desired temperature.

It is difiicult, according to this practice to insure that all parts of the pile have the same temperature. Unless the heating is carried on very slowly, the top of the box is generally heated more quickly than the'other portions thereof. The heat treatment effected,

therefore, isnot uniform and, in some cases, the material at the hotter portions of the pile is even over annealedso that it can not be used. lhe grain structure of the material at the top and bottom of the pile differs greatly and the resulting product is by no means of uniform characteristics. A variation of as much as 250 F. may be observed between the top and bottom of the pile if the heating is carried on rapidly. The demand for higher quality in the. roduct has necessitated that the heating e effected veryslowly to eliminate this difi'erence in temperature and the resulting differences in the characteristics of the finished material. This long period of treatment required reduces the output and increases the amount of equipment necessary.

I have invented a method and apparatus which permits the heating of the boxes containing the material to be annealed to be carried on at a high rate without the danger of overheatin or over annealing any portions of the pile. The'difierent portions of the pile are maintained at substantially the same temperature and are given a uniform heat treatment. Since the invention permits the heating to be effected at a greater rate, the output of a given amount of equipment is greatly increased. It also reduces the amount of fuel necessary for annealing a given amount of material.

According to the invention, I arrange a shield of a material having a low thermal 'rnaron. 1

ieea, Serial no. aaaiaa.

conductivity between portions of the pile of material and the enclosing box. This thermal insulating shield prevents overheating of those portions of the pile which have been observed to possess a tendency in this direction. In the usual instance, the insulating shield takes the form of one or more sheets of thermal insulating material such as asbestos paper. These'sheets are placed over the top of the pile of material to be annealed, with their ends overhanging the sides of the pile to form a curtain. in another form of the invention, ll provide a metal box with an open bottom and a lining of thermal insulating material. This box is placed over the top of the ile of sheets to be annealed and prevents t e overheating of this portion'of the pile.

For a complete understanding of the invention, reference is made to the accompanying drawing illustrating a present preferred embodiment of the invention. In the draw- Figures 4 and 5 are reproductions ofphoto- 30 micrographs showing the variation in grain structure which results from the non-uniform heat treatment of ferrous sheets according to the present practice of box annealing.

Referring in detail to the drawing and especially to Figure 1, a pile of metallic sheets is indicated at 10. The pile of sheets is su ported on an annealing box bottom 11. e top of the annealing box (not shown) is adapted to be lowered over the pile 10 and to rest on the bottom 11. In order to prevent overheating or over annealing of the sheets in the top of the pile, which is generally the hottest portion, I employ a plurality of strips 12 of material having low thermal conductivity such as asbestos. The ends of the strips hang down over the sides of the pile and form an insulating shield which obstructs the transfer of heat from the annealing box to the piled sheets.

The lower portions of the pile 10 are known to heat up more slowly than the top so that no insulating material need be placed around the bottom of the pile. It may be found, however, that, because of the construetion of the annealing furnace, or the method of heating it, certain portions of the pile other than the top will heat up more. rapidly than other portions. In such cases, I apply an insulating shield to any such portion of the pile of sheets to prevent overheating thereof. An insulating shield may, for exlining is by the use of expanded metal lath and asbestos plaster. The insulating lining extends down from the top of the box to within a short distance of the bottom thereof so that a continuous insulating shield is formed for the top of a pile of sheets. The

, application of the form of the invention shown in Figures 2 and 3 is the same as that shown in Figure 1. Instead of using the separate strips 12 to shield the top of the pile 10, the box 13 is lowered thereover. The top of the annealing box proper is, of course, lowered over the pile of sheets and the box 13 resting thereon so as'to enclose the whole assembly..

Figuresfi and 5 illustrate the difference in the grain structure of top and bottom sheets in a pile annealed by known methods. The product is obviously non-uniform and has widely varying characteristics. The present invention largely eliminates such differences and produces a pile of sheets having a high degree of uniformity in the grain structure and other characteristics of the sheets from the top to the bottom of the pile.

The invention is characterized by the fact that it permits the annealing of sheet, strip, or like material to be carried out more rapidly and more economically than heretofore,

. and, furthermore, it produces a product which is uniform and not subject tothe defects encountered in the product of other methods. Overheating of the sheets is minimized and a uniform product is obtained having the desired grain structure from the top to the bottom of the pile. Since the heating may be effected more rapidly Without overannealing the sheets by my method, the amount of fuel and the time required are substantially reduced. The output of an annealing furnace is thus increased markedly. The

temperature durin annealing is substantially uniform throug out the pile and it is not necessary, as heretofore, to lower the fur nace temperature to keep the sheets at the top of the pile from being over-annealed or overheated. Since the temperature of all parts ofthe pile is maintained substantially constant, the annealing temperature may be controlled within'a very narrow range by suitably controlling the annealing furnace. Another advantage of the invention is that, since the annealing is carried on more rapidly, the material is not maintained at annealing temperature long enough for excessive grain growth or the formation of brittle massive cementite to occur. Thus one of the causes-of defects in the product as now produced is eliminated. The invention permits the maximum flow of heat throu h the interior of the box, but prevents over eating of any portion thereof by making uniform the absorption of heat by difierent portions of pile of material. -By accurately controlling the temperaturefit is possible to produce a grain structure in the material which will impart the desired quality to the finished product. Y Y

I have described the invention as applied to the-annealing of sheets, but it is not limitd ed to sheets as the word is understood by the trade but includes all similar material such ask coiled or uncoiled strip, plates, and the Although I have described but two modifications of the invention, the specific details thereof do not limit the scope of the invention. Instead of asbestos paper or plaster, I may employ any other type of shielding material having a low thermal conductivity. The shield may be disposed wherever necessary to prevent overheating. The method may be employed for treatment of any type of relatively thin material. Since the invention may be practiced in forms other than those described, any changes in the modifications set forth ma be made without departing from the spirit of the invention or the scope of the appended claims. 1

I claim:

1. In the method of box annealing wherein the box is subjected to a non-uniform heating, which includes the step of uniformly heating the metal by heat insulating material between thebox and the metal therebyretarding the absorption of heat by the metal from the more highly heated portions of the annealing box but not all portions of the metal. I

2. In the method of box annealing metal the steps of enclosing stacked metal within an annealing box, heating the annealing box in such a manner that a certain portion of the box becomes more highly heated than other portions, causing the metal to be uniformly heated by interposingmaterial of relatively low heat conductivit between only the more highly heated portions of the box and the metal adjacent thereto.

3. In the method of box annealing sheet metal, the steps of enclosing stacked metal within an annealing box, heating the annealing box in such a manner that certain portions of the box become more highly heated than other portions, and protecting those portions of the sheet metal adjacent the more iighly heated portions of the box but not all portions of the metal from the radiated heat of the interior of the box by positioning relatively low heat conducting material within the interior of the box ad acent to the more highly heated portions of the box.

4. In the method of box annealing sheet metal the steps of enclosing stacked sheet metal within an annealing box and interposing material of relatively low heat conductivity between just the top portions of the box and the sheet metal adjacent thereto, thereby making substantially uniform the absorption of heat by the entire stack of sheets.

5. Ina device for box annealing-metal the.

combination of an annealing box adapted to have certain portions thereof become more highly heated and material of relatively low heat conducting properties positioned within the interior of the box adjacent such portions thereof which become more highly heated than others.

6. In a device for box annealing metal the combination of an annealing box and fibrous material of relatively low heat conducting properties positioned within the interior of the box juxtaposed with those portions of the box which become more highly heated.

7. In a device for box annealing metal the combination of an annealing box and material of relatively low heat conducting properties positioned Within the interior of the box adjacent just the top portions of the box which become more highly heated than others.

In testimony whereof I have hereunto set my hand.

JAMES A. SMAIL. 

